| OVERVIEW | ||
|---|---|---|
| Steaming lumber is common on certain species where a darkening effect can change the color, thereby increasing the value of the lumber. In addition, steaming has found new uses as part of the drying process, where shock steaming helps prevent color change in the later kiln drying process and it seems the lumber will have an initial and fast reduction in average moisture content even on species like red and white oak. In Europe one of the most common steamed species is beech. The color of beech can be manipulated from a very light (nearly white) to a dark brown, depending on the steam time, and the later drying schedule. Whereas in North America one of the most common steamed species is walnut, where the lumber company tries to darken the sapwood to the same color as the heartwood. Steaming lumber for color is not a difficult or complicated process; however, most lumber companies do not have adequate control over the process to insure a constant result throughout all four seasons of the year. It does matter if the lumber is warm or frozen when the steaming process is initiated. Kiln-direct's steam controller has been designed to cover all aspects of steaming lumber from shock steaming to color steaming and how it has been designed to eliminate the seasonal steaming variation found on traditional steaming installation. More detailed information can be found under these links: How much steam and pressure will you need. Without steam there is no steam chamber and it is essential to have adequate steam to insure that the final steaming temperature is reached in a timely period. How to load a steam chamber. The main question is whether to load it with deadpacked bundles or sticked bundles. How to build a steam chamber. Building a steam chamber seems simple, but building one that will last a long time is much harder. The climate inside a steam chamber is much tougher than a kiln and this must be taken into account. Can I use my kiln for steaming lumber. This can be done, but it will not give you the best result. |
| SHOCK STEAM LUMBER | ||
|---|---|---|
| Shock steaming is a term used for a short steam treatment which can be compared to a short heat treatment. The object of a shock steaming is to achieve a certain wood temperature as soon as possible and then stop the steam process either to prevent damage or a color change. Kiln-direct's steam controller used a special internal wood temperature sensor to help insure that the shock steaming is terminated after the wood has reached the desired set point. When shock steaming it is essential to only steam sticked bundles, since deadpacked bundles will not allow evenly steaming/heating of all the lumber. Benefits of shock steaming certain species. Beech (especially european). Help prevent later color damage during the drying process and has shown to immediately reduce the initial moisture content thereby both reducing the drying time and equalizing the moisture content. Oak. Shock steaming or oak has been mentioned as early as 1920's in some kiln drying literature about a short steam treatment, which could help reduce the drying defects in oak. This is not as well documented, but based on experience from Wooddryer System customers who shock steam oak regulary, we believe that you will see an initial drop in and equalization of the moisture content. When shock steaming a cubic meter of lumber you will probably use 150-200 kg steam (750-1000 lbs steam per 1000 bf.) through the whole shock steaming process. Kiln-direct believes shock steaming can help provide better drying results on several species. However, very little research and experimentation has been done on this. The lack of testing is probably due to the fact that few sawmills have special steam chambers on-site for testing. |
| COLOR STEAM LUMBER | ||
|---|---|---|
| Steaming for color is the best known reason for steaming and is most commonly done on beech (european) and walnut (american). On beech it is done to provide the customer with a certain color in the range from nearly white to dark brown, which will depend on the length of the steaming period. On walnut the reason is normally to darken the sapwood from its natural light color toward the darker heartwood, which is more valuable. Kiln-direct believes you will recieve the best steaming result if you choose to place the lumber on sticks. However, on steam treatments over 24-36 hours it is not as critical and you can choose to steam deadpacked bundles. Kiln-direct's steam controller has been designed to help you achieve the exact color you desire. Our controller prepares the load to a certain condition before moving into the steam process phase. The preparation prevents you from getting different results depending on the conditions of the lumber entering the steam chamber (frozen or not).
|
| SEASONAL STEAMING SOLUTIONS | ||
|---|---|---|
| How we avoid the seasonal steaming variations. This problem is most sevier when one tries to obtain a constant light coloring throughout the year. The problems comes for the conditions of the lumber at the loading of the steaming chamber, which on nearly all systems are also the conditions at the beginning of the steaming process. The two most extreme cases, a summer day with lumber, which is 27C (80F) outside and a winter day with lumber, which is frozen to -10C (14F). Logically it would make a difference if the steaming process is started at 27C or -10C, especially on shorter steaming schedules for lighter color, where the core temperature will be much lower on the frozen lumber when the chamber temperature has been reached. Solution by kiln-direct. First and foremost the steam chamber controllers design by kiln-direct prepares the lumber to a operator specified condition. These operator specified conditions will normally be 20C and a waiting period of one hour before initiating the actual steaming process. In addition, the operator will choose a minimum core temperature, which must be achieved before the controller will initiate to process. This minimum temperature is normally set at 5C or 40F. By going through a preparation period, where several parameters must be met is essenstial for contact steaming quality irregardless of the incoming conditions, you will eliminate or minimize the possibility of producing different colors when using the same steaming schedule. |
| USE LUMBER KILN FOR STEAMING | ||
|---|---|---|
| Using a regular kiln for steaming is possible, but not advisable, since it is not as efficient as a dedicated steam chamber and your quality (color) will probably vary more. In addition, a kiln is normally much larger than a steam chamber and most lumber companies can rarely fill up a complete kiln with lumber for steaming. Here are some of the major problems with using a kiln for steaming your lumber: Wasted space. A smaller closed room with little free space will require less energy and make it easier with a high relative humidity in the chamber. Not designed for live and constant steam pressure. A steam chamber is exposed to a constant steam pressure on all the walls, ceiling, joints, etc. in a way a kiln is not. This will normally result in steam penetrating into the walls and ceiling insulation. Too big. Most lumber companies cannot fill a regular kiln full of lumber, which need steaming. Also, even it you could accumulate sufficient quantity, it will probably take several day. This is not optimum, since the best steam result is achieved if the steaming process is initiated within 24 hours of being sawn. |
| LOADING A STEAM CHAMBER | |||||
|---|---|---|---|---|---|
|
|||||
| STEAM REQUIREMENTS | |
|---|---|
| Providing adequate steam supply is important when steaming for color, but ESSENTIAL when you are shock steaming. When you are shock steaming your objective is to reach a certain internal wood temperature as soon as possible and return the lumber to normal temperatures again without any (or miminum) color change or degrade. If the steam chamber is unable to reach the desired temperature in a short period the lumber will begin to change color or generate degrade, which is exactly what the we are trying to prevent. Steam supply requirement. Steam pressure requirement. Low pressure steam is the best, since it is not as overheated as high pressure steam, when released into the near zero pressure environment of the steam chamber. The high pressure steam will create more heat with less moisture added to the air, which will result in a lower relative humidity. Higher relative humidity help prevent degrade. Metric: Best steam supply pressure is 0.5 bar (mainimum 2-3 bar). Imperial: Best steam supply pressure is 8 psi (maximum 30-45psi). Steam volume requirement. As mentioned earlier steam volume is important (especially when shock steaming) for insuring a good steaming result. The amount of steam you can supply the steam chamber is nearly directly related to the time it take reach your final steam treatment temperature. Simply put more steam input equals more energy released into the chamber for heating the lumber. More steam supply = shorter heating period. Metric: Rule of thumb: Minimum 60 kg steam/hour per cubic meter of lumber. Imperial: Rule of thumb: Minimum 300 lbs steam/hour per 1000 boardfeet of lumber. |
| CONSTRUCT A STEAM CHAMBER | ||
|---|---|---|
| Building your own steam chamber is definitely the most economically way, either with on-site or local personnel. Kiln-direct are here to help you in this process. It is important to understand that the environment in a steam chamber is significantly harder on the building than those in a standard kiln. First you have a building which cycles between regular outside temperature and new boiling temperatures much more frequently than a kiln (every one to two days). Secondly, you must consider that chamber has an inside pressure which tries to push this harsh climate conditions into the walls and roof system. Description of the general components of a steam chamber: Building and foundation. Please look further down on the page regarding your general choices and there advantages and short comings. Water trench in the floor. This trence is normally located near the back wall and the side walls. It purpose is to collect the condensate, "juices" from the lumber, and trash. A drain pipe is placed about 150-300mm (6"-12") above the bottom of the trench. Steam supply pipe. This or these pipe are normally 75-100mm (3"-4") diameter with hole evenly spaced down the length of the pipe. The best material for the steam pipe is stainless steel, which minimizes iron stain on species, such as oak. These pipes are normally installed cross ways in the steam chamber, the key to place these pipes to insure as even steam distribution as possible. The holes in the pipe increases in size in the same direction as the steam is moving. The smaller holes in the begging and the larger ones in the end insures move evenly steam distribution as the pressure becomes lower as it passes the first holes. Steam control system. Some kilns use a simple temperature and time delay function which is essential, but a more advanced controller can help you achieve constant and better results everytime. Venting pipe. This is normally located in the middle of the back wall near the floor level. This pipe is normally a 38-50mm (1.5"-2") stainless steel pipe with unrestricted access to the outside. The purpose of this vent pipe is to release the excess steam to prevent too much pressure buildup, which would increase the pressure on the wall and the likeliness of excessive moisture penetration into the walls and ceiling. Main door system. It is important that the main door seals tightly against the door frame and it helps reduce your energy consumption, especially on longer steam treatment schedules. We can only advise you to install some kind of a 100% stainless steel door system with 100-150mm (4"-6") of insulation. The outside can be aluminum profile sheeting, but not regular metal sheeting. This leaves you with three general choices in building a steam chamber: Highest quality for long term use. -- Concrete walls and stainless steel roof steam chamber. -- All stainless steel steam chamber.(Kiln-direct sells complete small steam chambers) -- Concrete and/or concrete masonry steam chamber. Low quality for short term use. Wood panel construction (Approx 5 years life span with daily use). Use old refrigerated container. |